Mitochondrial DNA from three somatic hybrid cell lines of Pennisetum americanum + Panicum maximum was compared with mitochondrial DNA of the parents. Gel electrophoresis of BamHI-restricted mitochondrial DNA indicated that extensive rearrangements had occurred in each of the three hybrid lines. The hybrid restriction patterns showed a combination of some bands from each parent plus novel fragments not present in either parent. Additional evidence for rearrangements was obtained by hybridization of eight DNA probes, carrying sequences of known coding regions, to Southern blots. Each of the somatic hybrids exhibited a partial combination of the parental mitochondrial genomes. These data suggest recombination or amplification of the mitochondrial genomes in the somatic hybrids.